The present invention concerns an improvement to drive apparatus, generally referred to as contra-angle handpieces, for rotary tools used in surgery, and in particular, in dental surgery.
Such contra-angle handpieces are generally made up of an anterior part or “neck” having a cylindrical and/or conical external shape, for supporting the head which is to receive the dental instrument, and a posterior part or “handle” having a shape which is substantially cylindrical and/or conical in revolution.
The handle includes a mechanical connection to a dental drive motor. At the opposite end from the connection to the motor, the handle is connected to the neck of the contra-angle handpiece.
The neck has an axis which intersects with the axis of the handle, and which is positioned at approximately 20 degrees relative to the axis of the handle, in such a way as to form a bend or contra-angle. The axis of the dental instrument is perpendicular to the axis of the neck, and the dental tool is generally oriented in the direction of the axis of the handle.
The assembly comprised of the handle, the neck and the head contains a kinematic chain, the object of which is to transmit rotation of the motor's shaft to the dental instrument. This can possibly include a reduction or multiplication of the speed of rotation of the dental instrument.
In view of the above-described angle, and contra-angle structure, the kinematic chain is also made up of three parts. A first part is arranged in the handle, a second part is arranged in the neck, and a third part is arranged in the head. The third part of the kinematic chain is also equipped with removable or non-removable means for fixing a dental instrument to the handle, for driving the dental instrument in rotation and for stopping translational movement of the instrument along the axis of the head.
Generally speaking, rotational movement is transmitted between these different parts by gears having non-parallel axes. The position of these non-parallel axes is of great importance, on the one hand, in terms of the useful life of the contra-angle handpiece (poor positioning being reflected in premature wear of the pinions) and, on the other hand, in terms of comfort for the patient and for the dental surgeon (poor positioning being reflected in excessive noise). This is particularly so in view of the fact that the speeds of rotation are presently 40,000 rpm.
Thus, the positioning of each part of the kinematic chain is generally such that each of the parts is fixed in the respective parts of the contra-angle handpiece (handle, neck, head) so as to form an integral body, in this way constituting an independent sub-unit.
Although such apparatus are satisfactory, the means of fixing the elements of the kinematic chain are complex. Consequently, restoration of the components by replacing them is virtually impossible for non-specialists.